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Income Taxes (Reasonable Probablity of Tax Benefit) (Details) - CAD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2017 | Dec. 31, 2018
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued [Abstract] |  |
Accrued interest | $ 1 | $ 4
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items] |  |
Temporary Differences/Potential change | 822 | $ 1,400
Settlement with Taxing Authority [Member] | 2006 through 2010 years [Member] | Nova Scotia Power Inc. [Member] | Canada Revenue Agency [Member] |  |
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items] |  |
Net amount in dispute | 62 |
Prepaid amount in dispute | $ 23 |

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- Definition The amount of the unrecognized tax benefit of a position taken for which it is reasonably possible that the total amount thereof will significantly increase or decrease within twelve months of the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32718-109319 + Details
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- Definition Amount of interest expense accrued for an underpayment of income taxes. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32718-109319 + Details
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